With rapid development of a packet service and an intelligent terminal, a high-speed service with a large data amount has an increasing requirement for a spectrum. According to the latest released FCC international spectrum white paper, unlicensed spectrum resources are more than licensed spectrum resources. Unlicensed spectrums include frequency bands used for devices in industrial, scientific and medical (ISM, Industrial, Scientific and Medical) fields and the like. For example, there are three frequency bands in the United States: 902-928 MHz, 2400-2484.5 MHz, and 5725-5850 MHz; and a frequency band of 2.4 GHz is an ISM frequency band common to all countries. Technologies used on an ISM frequency band mainly include wireless fidelity (WiFi, Wireless Fidelity), wireless local area network (WLAN, wireless local network), Bluetooth, and Zigbee (Zigbee), and the like. WiFi is based on the Institute of Electrical and Electronics Engineers (IEEE, Institute of Electrical and Electronics Engineers) 802.11 family of standards, such as 802.11a, 802.11n, and 802.11ac. WiFi has relatively low efficiency in terms of quality of service (QoS, quality of service), multi-user scheduling (scheduling), or the like, and a mobility management (mobility management) function is limited.
A licensed-assisted access (LAA, licensed assisted access) of a Long Term Evolution Advanced (LTE-A, Long Term Evolution Advanced) research project of the 3rd Generation Partnership Project (3GPP, the 3rd generation partnership project) is studying to apply an LTE-A cellular communications technology on an unlicensed frequency band, so as to use the unlicensed frequency band resources more effectively, and increase an available spectrum bandwidth of an LTE user. As shown in FIG. 1a and FIG. 1b, the LAA is based on a scenario in which carrier aggregation (CA, Carrier Aggregation) is performed on a licensed spectrum and an unlicensed frequency band. A carrier on the licensed spectrum is used as a primary serving cell (PCell, Primary cell), and a carrier on the unlicensed frequency band is used as a secondary cell (SCell, Secondary Cell). The PCell and the SCell in the LTE-A CA may use a collocation site (collocate or co-site) or non-collocation sites. For example, when non-collation sites are used, an evolved NodeB (eNB) and a remote radio head (RRH, Remote Radio Head) respectively provide the PCell and the SCell. The PCell is a cell (cell) that initially accesses a system when user equipment (UE, User Equipment) performs a random access procedure (random access procedure), or a cell that accesses a target base station when user equipment performs a handover procedure (handover procedure). The PCell further provides security (security) and non-access stratum (NAS, Non-Access Stratum) signaling transmission. The SCell mainly provides additional radio resources for data transmission.
LTE-A dual connectivity (DC, Dual Connectivity) indicates that carriers that are used for carrier aggregation for the UE are provided by different base stations. The UE can simultaneously or separately communicate with two base stations, so as to improve a peak rate and a throughput at a cell edge. Generally, a connection between base stations is a non-ideal backhaul link (backhaul), that is, message exchange between base stations requires a specific delay, and a limitation is also imposed on a capacity. Base stations participating in the LTE-A DC include a master eNodeB (MeNB, Master eNB) and a secondary eNodeB (SeNB, Secondary eNB). The master eNodeB provides the PCell, and optionally, provides another SCell. The secondary eNodeB provides a primary secondary cell (PSCell, Primary Secondary Cell), and the PSCell supports a physical uplink control channel (PUCCH, Physical Uplink Control Channel), and optionally, supports another SCell. The master eNodeB provides the UE with a base station connected to an S1-mobility management entity (S1-MME) interface. The secondary eNodeB is mainly configured to provide additional radio resources for data transmission.
In a case of performing carrier aggregation on a licensed LTE cell and an unlicensed LTE cell configured on a terminal, the terminal does not perform radio link monitoring on the unlicensed LTE cell. When the terminal is configured to independently use the unlicensed LTE cell, or the terminal is configured to perform inter-base station dual connectivity on the licensed LTE cell and the unlicensed LTE cell, if the terminal does not perform radio link monitoring on the unlicensed LTE cell, the following problem cannot be found in a timely manner: a radio channel of the unlicensed LTE cell cannot provide the terminal with a transmission service due to deterioration, and consequently, communication quality of the terminal is reduced and even interrupted, and user experience is seriously affected.